Getting Unkown error when installing MQTT Connector with confluent-hub install behind a firewall

[langalibalele]

I expanded the connect container in docker-composite.yml in order to install, create and deploy the MQTT Connector (kafka-connect-mqtt):
[see Apache Kafka / Kafka Connect / MQTT / Mosquitto Live Demo]

` command:
- bash
- -c
- |
# Install connector plugins
# This will by default install into /usr/share/confluent-hub-components/ so make
# sure that this path is added to the plugin.path in the environment variables
confluent-hub install --no-prompt confluentinc/kafka-connect-mqtt:latest
# Launch the Kafka Connect worker
/etc/confluent/docker/run &

    echo "Waiting for Kafka Connect to start listening on localhost:8083 ⏳"
    while : ; do
        curl_status=$$(curl -s -o /dev/null -w %{http_code} http://localhost:8083/connectors)
        echo -e $$(date) " Kafka Connect listener HTTP state: " $$curl_status " (waiting for 200)"
        if [ $$curl_status -eq 200 ] ; then
        break
        fi
        sleep 5
    done
    echo -e "\n--\n+> Creating Kafka Connect source connectors"
    # Create a Kafka Topic for consuming the MQTT messages via the MQTT Connector (needs to be the same as in the Connector Config):
    #kafka-topics --create --bootstrap-server 127.0.0.1:9092 --replication-factor 1 --partitions 1 --topic mqtt.temperature
    #curl -s -X POST -H "Content-Type:application/json" --data @/c/temp/mqttconnector/mqtt-connector-config.json http://connect:8083/connectors
    echo -e "\n--\n+> config mqtt connector"
    curl -s -X POST -H 'Content-Type: application/json' http://localhost:8083/connectors -d '{    "name" : "mqtt-source",	"config" : {		"connector.class" : "io.confluent.connect.mqtt.MqttSourceConnector",		"tasks.max" : "1",		"mqtt.server.uri" : "tcp://10.230.145.42:1883",		"mqtt.topics" : "temperature",		"kafka.topic" : "mqtt.temperature",		"io.confluent.topic.bootstrap.servers": "broker:29092",		"io.confluent.topic.replication.factor": "1",		"io.confluent.license":""    }}'
    echo -e "\n--\n+> test mqtt connector"
    #kafka-topics --create --bootstrap-server broker:29092 --replication-factor 1 --partitions 1 --topic mqtt.temperature
    #kafka-console-consumer --bootstrap-server broker:29092 --topic mqtt.temperature --property print.key=true --from-beginning
    #curl -s -X POST -H 'Content-Type: application/json' http://connect:8083/connectors -d
    
    # Don't exit
    sleep infinity`

When directly conected to the internet, docker-compose up -d yields correct installation under the conect container:

Downloading component Kafka Connect MQTT 1.4.0, provided by Confluent, Inc. from Confluent Hub and installing into /usr/share/confluent-hub-components Adding installation directory to plugin path in the following files: /etc/kafka/connect-distributed.properties /etc/kafka/connect-standalone.properties /etc/schema-registry/connect-avro-distributed.properties /etc/schema-registry/connect-avro-standalone.properties Completed Waiting for Kafka Connect to start listening on localhost:8083 ⏳ .... Thu Feb 4 19:44:40 UTC 2021 Kafka Connect listener HTTP state: 000 (waiting for 200)

When connecting through our company firewall, calling docker-compose up -d yields the follwing in the connect container:
Downloading component Kafka Connect MQTT 1.4.0, provided by Confluent, Inc. from Confluent Hub and installing into /usr/share/confluent-hub-components javax.net.ssl.SSLHandshakeException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target Error: Unknown error Waiting for Kafka Connect to start listening on localhost:8083 ⏳

I have not found a solution to this yet. Apparantly adding the *.confluent.io cert to java cacerts does not resolve the issue. I suspect the firewall is blocking download of the jar files in \lib of the connector